Chemical-mechanical planarization (“CMP”) processes are frequently used to planarize the surface layers of a wafer in the production of ultra-high density integrated circuits. In typical CMP processes, a wafer is pressed against a slurry on a polishing pad under controlled chemical, pressure, velocity, and temperature conditions. Slurry solutions generally contain small, abrasive particles that mechanically remove the surface layer of the wafer, and chemicals that chemically remove the surface layer. The polishing pad is generally a planar pad made from a relatively soft, porous material, such as blown polyurethane. After the wafer is planarized, it is cleaned to remove residual particles on the surface of the wafer that were introduced to the CMP process by the slurry, polishing pad, or wafer.
CMP processing is particularly useful for planarizing a metallic surface layer to form conductive features, such as interlayer connectors and/or conducting lines. Interlayer connectors are fabricated by forming holes through a dielectric layer, depositing a very thin titanium liner over the dielectric layer and in the holes, depositing a layer of metallic material over the titanium liner and in the holes, and then planarizing the metallic layer to an end-point just below the upper surface of the dielectric layer. Conducting lines are created by forming parallel channels in a substrate, depositing a very thin titanium liner over the substrate and in the channels, depositing a layer of metallic material over the titanium liner and in the channels, and then planarizing the metallic layer to an end-point below the top of the substrate. The metallic layers of material are desirably planarized using slurries that contain abrasive particles made from aluminum oxide (Al2O3). After the metallic layers are planarized, residual materials from the slurry, polishing pad, or wafer remain on the planarized surface of the wafer. The residual materials are commonly aluminum oxide particles from the slurry and titanium accumulations from the titanium liner, both of which cause defects in the wafer. Thus, it is necessary to clean such residual materials from the planarized surface of the wafer.
One problem with current post-CMP cleaning processes is that they still allow a significant number of defects to remain on each wafer. In a typical post-CMP cleaning process, the wafer is placed in a bath of deionized water that is vibrated with sonic energy. The sonic deionization bath removes the loose residual particles of aluminum oxide from the surface layer of the wafer, but it does not remove the residual titanium accumulations. The sonic deionization bath produces a wafer surface that has approximately 20 to 30 defects per wafer. To remove the residual titanium accumulations from the planarized surface, the wafer is dipped in hydrogen fluoride solution (“HF solution”) that etches the residual titanium accumulations and some of the oxide from the surface of the wafer. Although the HF solution removes the residual titanium accumulations, it also produces new defects in the wafer so that the resulting wafer surface has 300 to 400 defects per wafer. Accordingly, it would be desirable to develop a method that removes both the residual titanium accumulations and other residual materials from a planarized wafer to produce a wafer surface that has less than fifty defects per wafer.